1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic process such as a copier, a printer or a facsimile apparatus, and particularly to cleaning means for a transfer material or developer image bearing and conveying member in the image forming apparatus.
2. Related Background Art
In recent years, compound machines having all of output terminals such as a copier, a printer and a facsimile apparatus have come to be widely accepted in the market. Image forming apparatuses using the electrophotographic process have been widely accepted as such output terminals coping with the network, but the limited number of sheets for which the main body continues to operate normally without maintenance, i.e., the so-called duty cycle, has been mentioned as a great problem. The greatest rate controlling of the duty cycle is the life of an image bearing member, and from the viewpoint of ecology, it has become a great task to eliminate waste, that is, the decrease expendables, to extend the lives of the expendable, improve reliability, etc.
Also, the digitization of conventional analog apparatuses has been advanced, and it has also become a task to make the cost of the main body equivalent to or less than that of the analog apparatus. Further, black-and-white machines have been in the mainstream not only in conventional copiers and printers, but in offices as well, the full coloration of originals or output files is increasing rapidly. Accordingly, not only the digital machines equivalent to black-and-white printers, reducing the cost of the main body and running cost has become a task. For this reason, there has been desired a technique which can epoch-makingly reduce TCO (total cost of owners, i.e., total necessary cost as viewed from the user).
In such a situation, in recent years, the mainstream has been occupied by a color image forming apparatus which is provided with a plurality of photo-sensitive drums and a transfer belt for bearing and conveying a recording material, and sequentially superimposes and transfers toner images of different colors formed on the respective photosensitive drums to the recording material borne on the transfer belt to thereby obtain a color image, i.e., a so-called four-station tandem type color image forming apparatus.
Also, in the above-described image forming apparatus, various adhering materials (such as toners scattering from the photosensitive drums, toners transferred from the photosensitive drums during jam or at the time between a sheet and a sheet, and mold releasing oil adhering to the recording material during the toner image fixation on a first surface when image formation is effected on a second surface of the recording material) adhere onto the transfer belt as a recording material bearing member and therefore, it has been proposed to provide as cleaning means a counter blade system, a fur brush system, an oil cleaner roller for removing the mold releasing oil, an oil cleaner web or the like. There has also been proposed a toner manufactured by the polymerizing method having oil internally added which need not use such mold releasing oil.
An example of such image forming apparatus in which a recording material such as paper is attracted to and conveyed by a transfer belt (endless belt) as a recording material bearing member and image formation is effected will now be described briefly with reference to FIG. 6 of the accompanying drawings.
The image forming apparatus is provided with a photosensitive drum 205 therein, and a toner image is formed on the photosensitive drum 205. A transfer belt 206 as a recording material bearing member is installed adjacent to the photosensitive drum 205, and the toner image formed on the photosensitive drum 205 is transferred onto a recording material P borne on and conveyed by the transfer belt 206. The recording material P to which the toner image has been transferred has the toner image thereon fixed by heating and pressurizing in a fixing device 209, whereafter it is discharged out of the apparatus as a recorded image.
An exposure lamp 201, a photosensitive drum charger 202, an exposure device 203, a developing device 204, a transfer charger 207 and a cleaner 208 are provided around the photosensitive drum 205, and although not shown, a light source device and a polygon mirror are further installed in the upper portion of the apparatus.
A laser beam emitted from the light source device is scanned by the rotating polygon mirror, and the scanned beam is deflected by a reflecting mirror, and is condensed on the generatrix of the photosensitive drum 205 by an f"THgr" lens and the photosensitive drum 205 is exposed to the light, whereby a latent image conforming to an image signal is formed on the photosensitive drum 205.
The developing device 204 is filled with a predetermined amount of toner by a toner supplying device, not shown. The developing device 204 develops the latent image on the photosensitive drum 205 and visualizes it as a toner image.
The recording material P is contained in a recording material cassette, not shown, and is supplied therefrom to the transfer belt 206 via a plurality of conveying rollers and registration rollers 213, and is sequentially fed to a transfer position opposed to the photosensitive drum 205 by the conveyance by the transfer belt 206.
The transfer belt 206 is formed of a material comprising a dielectric material resin sheet such as a polycarbonate resin sheet, a polyethylene terephthalate resin sheet (PET resin), a polyvinylidene fluoride resin sheet, a polyurethane resin sheet, a polyamide resin sheet or a polyimide resin sheet having a resin filler such as carbon black dispersed therein, and having its volume resistivity adjusted to the order of 107-1015 xcexa9cm, and use is made of a belt having its opposite end portions superposed upon each other and joined together, and made into an endless shape, or a belt having no seam (seamless).
This transfer belt 206 is rotated by a driving roller 211 and when it reaches a predetermined speed, the recording material P is fed out from the registration rollers 213 to the transfer belt 206, and the recording material P is conveyed toward the transfer position. At the same time, an image writing signal becomes ON, and with it as the reference, image formation is effected on the photosensitive drum 205 at predetermined timing. Then, at the transfer position under the photosensitive drum 205, the transfer charger 207 imparts an electric field or charges, whereby the toner image formed on the photosensitive drum 205 is transferred to the recording material P. The recording material P, when fed out from the registration rollers 213 onto the transfer belt 206, is immediately nipped with the transfer belt 206 by and between an attracting charger 214 and an attracting charger opposite roller 215, and an electric field or charges are induced by the attracting charger 214, whereby the recording material P is electrostatically held on and conveyed by the transfer belt 206.
As the transfer charger 207, use is made of a non-contact charger such as a corona discharger, or a contact charger using a charging member such as a charging roller, a charging brush or a charging blade. The non-contact charger suffers from the problem that ozone is created, and the problem that charging is done through the air and therefore such charger is weak to the environmental fluctuations of temperature and humidity and images are not formed stably. On the other hand, the contact charger has the merit that ozone is not created and the charger is strong to the environmental fluctuations of temperature and humidity.
Next, the recording material P to which the toner image has been transferred has its charges eliminated in the downstream portion of the transfer belt 206 with respect to the direction of conveyance by a separating charger 216 and has its electrostatic attraction attenuated, whereby it leaves the distal end of the transfer belt 206. Particularly in a low humidity environment, the recording material is dry and electrical resistance becomes high and therefore, the electrostatic attraction between it and the transfer belt becomes great, and the effect of the separating charger 216 becomes great. Usually, the separating charger 216 eliminates the charges of the recording material P with the toner image thereon unfixed and therefore, a non-contact charger is used as the separating charger. As the output of the separating charger 216, use is made of an AC voltage of the order of Vpxe2x88x92p=10 kV and 500 Hz. Also, in order to prevent a bad image such as the scattering of the toner, a plus or minus DC component of the order of 100 xcexcA is sometimes superimposed on the aforementioned AC output.
The recording material P having left the distal end of the transfer belt 206 is conveyed to the fixing device 209. The fixing device 209 is comprised of a fixing roller, a pressure roller, a heat-resisting cleaning member for cleaning each of them, a heater installed in each roller, an applying roller for applying mold releasing oil such as dimethyl silicon oil to the fixing roller, a reservoir for the oil and a thermistor for detecting the surface temperature of the pressure roller and controlling the fixing temperature. The toner image formed on the recording material P is fixed on the recording material P by fixing, whereby a copy image is formed, and the recording material P is discharged onto a discharge tray.
After the transfer has been completed, the photosensitive drum 205 has any untransferred toner thereon removed by the cleaner 208, and is continuedly prepared for the next latent image formation.
The transfer belt 206 after the recording material P has been separated therefrom is being contacted by an electrically conductive fur brush 210 grounded to the recording material bearing side and the driving roller 211 grounded as a member opposed thereto to thereby remove any toner residual on the transfer belt 206 and other foreign substances and eliminate the accumulated charges thereon. As the electrically conductive fur brush 210, use can also be made of an electrically conductive web (unwoven fabric).
Further, numerous propositions have heretofore been made as the cleaning means, but means for scraping off the residual toner by a cleaning blade formed of an elastic material such as urethane rubber is simple and compact in construction and low in cost and moreover excellent in the toner removing function and therefore is widely put into practical use. As the rubber material of this cleaning blade, use is generally made of urethane rubber having high hardness and moreover rich in elasticity and excellent in wear resistance, mechanical strength, oil-resisting property, ozone-resisting property, etc.
While in the image forming apparatus as described above, a pair of rollers comprising the attracting charger 214 and the attracting charger opposite roller 215 are used as electrostatic attracting means for the recording material P, a non-contact charger such as a corona discharger or a contact charger using a charging member such as a charging roller, a charging brush or a charging blade may of course be used as the electrostatic attracting means as in the case of the transfer charging means. However, when the non-contact system is used, the state of contact between the recording material P and the transfer belt 206 is not ensured and therefore, it is necessary to provide a pressure member discretely to thereby secure the close contact between the recording material P and the transfer belt 206.
To effect it stably to electrostatically attract and convey the recording material P as described above, the attraction and charging of the entire width of the recording material P is necessary as a matter of course.
However, there are the following problems when as in the above-described example of the conventional art, a cleaning blade which contacts with the surface of the transfer belt 206 to thereby effect cleaning is used as the cleaning means for the transfer belt 206.
Firstly, it has been confirmed by an experiment that the frictional force by the cleaning blade between the transfer belt and the residual substances on the transfer belt is increased by endurance. This is considered to be that the degree of close contact and affinity between the cleaning blade and the surface of the transfer belt rise by the filming film on the surface of the transfer belt formed by endurance and raise the frictional force. This rise of the frictional force is considered to mean that the shearing stress of the cleaning blade, the shearing stress between the toners and the shearing stress near the surface of the transfer belt rise.
As the result, it is considered to lead to the turning-up (wire edge) of the cleaning blade, the chipping (localized edge breakage) of the cleaning blade, the occurrence of the fusing bond of the toner by an increase in the amount of generated heat by an increase in permanent strain shearing stress, and the occurrence of an increase in the fatigue wear by such an increase in the internal stress of the transfer belt as leads to the breakage of the transfer belt. Also, by an increase in the frictional force, there comes out the possibility of the driving load of the transfer belt increasing to thereby hinder the operation of driving a motor. Also, if the abrasion wear of the transfer belt becomes great, there is the possibility that the film thickness of the transfer belt itself decreases and the interchange of the transfer belt must be done frequently.
Secondly, in recent years, the above-described image forming apparatus has come to be widely used not only as the function of only a copier, but as a printer as described above. Also, the repletion of applications such as the feeder function and the sorter function has been advanced and a continues operation for 4,000 sheets or more has become possible as a job. For example, in the case of a 50 sheets/A4 machines, a continuous operation is performed for 80 minutes or longer if simply calculated. Under such a situation, it is considered that the atmospheric temperature near the cleaning blade reaches nearly 50xc2x0 C. and the contact (nip) portion between the cleaning blade and the surface of the photosensitive drum reaches a temperature higher than that. This leads to the problem that the frequency with which the adhesion or agglutination of the residual substances occurs on the surface of the transfer belt becomes high and the coefficient of friction g of the surface of the transfer belt is caused to rise.
Thirdly, as the particle diameter of the toner becomes smaller, development excellent in dot reproducibility and resolution can be accomplished and the sharpness and quality of toner images are improved, but again in this case, the specific surface area becomes large and therefore, the adhesion of the toner per unit weight to the transfer belt becomes great and the cleanability of the transfer belt may be aggravated. As the particle diameter of the toner becomes still smaller, the fluidity of the toner is aggravated and therefore, a greater amount of additive is required, and this leads to the problem that the wear or breakage of the cleaning blade as noted above and the localized streaky scratches on the surface of the transfer belt occur.
Fourthly, in recent years, polymer toner is being diversified for the improvement in transfer efficiency and the elimination of a releasing agent in fixation. However, the toner manufactured by the polymerizing method is generally high in sphericity. If this sphericity increases, the slipping-out of the toner may often occur in the heretofore generally used counter blade system to thereby cause localized shearing forces to be applied to the cleaning blade and cause the edge breakage of the blade.
So, the present invention has been made in view of the above-noted problems and the object thereof is to provide an image forming apparatus in which the excessive wear of a bearing and conveying member is prevented and yet a stable cleaning operation can be performed.
The image forming apparatus of the present invention for achieving the above object is provided with image forming means for forming an image by a developer, a bearing and conveying member capable of bearing thereon and conveying a transfer material on which the developer image is formed or the developer image directly transferred thereto, and cleaning means for cleaning the bearing and conveying member, the cleaning means having a cleaning blade abutting against the bearing and conveying member, and holding means holding the cleaning blade and swingable about a rotary shaft, wherein the angle formed by a tangential line on the abutting portion of the cleaning blade against the bearing and conveying member and a line linking the center of the rotary shaft and the abutting portion together is designed to be equal to or greater than 0xc2x0 and equal to or smaller than 15xc2x0, wherein said bearing and conveying member has physical property values of a Young""s modulus of 2.5xc3x97104 kgf/cm2 or greater and a tensile strength of 1,000 kgf/cm2 or greater, and the abrasion wear of the surface of the bearing and conveying member when in the used state of the apparatus, the bearing and conveying member has made 10,000 revolutions is equal to or greater than 0.01, xcexcand equal to or less than 1.0 xcexcm.
Another preferred form of the image forming apparatus is provided with image forming means for forming an image by a developer, a bearing and conveying member capable of bearing thereon and conveying a transfer material on which the developer image is formed on the developer image directly transferred thereto, and cleaning means for cleaning the bearing and conveying member, wherein the cleaning means is such that the abutting pressure of the cleaning blade thereof abutting against the bearing and conveying member is equal to or greater than 15 gf/cm and equal to or less than 100 gf/cm, the initial surface roughness Rz of the bearing and conveying member is equal to or greater than 0.01 xcexcm and equal to or less than 1.0 xcexcm, wherein said bearing and conveying member has physical property values of a Young""s modulus of 2.5xc3x97104 kgf/cm2 or greater and a tensile strength of 1,000 kgf/cm2 or greater, and the surface roughness Rz of the bearing and conveying member when in the used state of the apparatus, the bearing and conveying member has made 10,000 revolutions is equal to or greater than 0.01 xcexcm and equal to or less than 1.5 xcexcm.
Still another form of the image forming apparatus is provided with image forming means for forming an image by a developer, a bearing and conveying member capable of bearing thereon and conveying a transfer material on which the developer image is formed or the developer image directly transferred thereto, and cleaning means for cleaning the bearing and conveying member, wherein the cleaning means is such that the abutting pressure of the cleaning blade thereof abutting against the bearing and conveying member is equal to or greater than 15 gf/cm and equal to or less than 100 gf/cm, wherein said bearing and conveying member has physical property values of a Young""s modulus of 2.5xc3x97104 kgf/cm2 or greater and a tensile strength of 1,000 kgf/cm2 or greater, and the abrasion wear of the surface of the bearing and conveying member when in the used state of the apparatus, the bearing and conveying member has made 10,000 revolutions is equal to or greater than 0.01 xcexcm and equal to or less than 1.0 xcexcm.